This invention relates to coating compositions comprising hydroxy functional film former and an improved stable flow control additive which substantially reduces or eliminates settling and separation of the flow control additive from the composition. More particularly, the invention relates to such coating compositions containing flow control additive of the type comprising crosslinked dispersions containing microgel particles, which are prepared by addition polymerization of (a) first and second ethylenically unsaturated monomers each bearing functionality capable of crosslinking with the other and (b) at least one other monoethylenically unsaturated monomer, in the presence of (I) organic liquid which is a solvent for the polymerizable monomers, but a non-solvent for the resultant polymer and (II) a polymeric dispersion stabilizer which bears pendent ethylenic unsaturation capable of reacting with monomers employed in the addition polymerization. Still more particularly, the invention relates to such compositions including the stable crosslinked dispersions wherein the polymeric dispersion stabilizer comprises a random copolymer segment of ethylenically unsaturated monomers, some of which are characterized in that homopolymers thereof would be substantially insoluble in the organic liquid used to form the stable dispersion and some of which are characterized in that homopolymers thereof would be substantially soluble in the organic liquid used to form the stable dispersion. Even still more particularly, the invention relates to such compositions wherein the flow control additive comprises such stable crosslinked dispersions which are further stabilized by an additional stabilizer which, except for solvents, consists essentially of butylated melamine formaldehyde resin. Preferred compositions including the stabilized flow control additive are intermediate and high solids thermosetting compositions which are adapted to provide an automotive topcoat demonstrating hardness, high gloss, outstanding durability and excellent resistance to solvents and water.
Because of increasingly strict solvent emission regulations in recent years, low solvent emission paints have become desirable. A number of intermediate and high solids paint compositions have been proposed to meet these low solvent emission requirements. However, many of these compositions are deficient because of difficulty in application, poor flow out, lack of smoothness and evenness and poor distribution of pigment, particularly metallic flake pigments. the deficiency in compositions including metallic flake results from undesired reorientation of the metallic flake during application and curing of the coating. Flake reorientation results primarily because of the very low viscosity resins used in paint compositions to accommodate intermediate and high solids. The viscosity of these resins is not sufficient to immobilize the flakes which tend to redistribute themselves to show "reverse flop" and non-uniform distribution.
The preferred coating compositions of this invention, as a result of the improved flow control additive component thereof, combine desirable properties, including lower solvent content and low application viscosity, while also overcoming deficiencies of some of the previously proposed imtermediate and high solids materials, thereby achieving intermediate and high solids coating compositions particularly adapted for automotive topcoats including metallic flake as pigment.